The Fates (Morai in Greek) were either children of Nyx and Erebus or of Zeus and Themis. There were three sisters, Klotho, who spun the thread, Lachesis, who measured the thread, and Atropos, who cut the thread. The sisters were usually portrayed as old hags.
The Fates were even more powerful than the gods, though this did not stop the gods from trying. Homer writes it was the will of fate that the Greeks destroy Troy, when Rumor and Panic caused the Greeks to want to flee.
Aeneas was fated to go to Italy, despite the best efforts of Hera. Hera's actions in attempting to defy fate led to a premature death of Dido, the queen of Carthage. Since her thread was not cut to so short a length, she would not die even though a dagger had pierced her breast.
The Roman name for the Fates is the Parcae, originating from the Latin word parere - to to bring forth.